Update from https://crrev.com/328418

base/message_loop/incoming_task_queue.cc

Index: base/message_loop/incoming_task_queue.cc
diff --git a/base/message_loop/incoming_task_queue.cc b/base/message_loop/incoming_task_queue.cc
index c1ce939b0c4708ac431d80b54a35ee8ef73b314c..5e9a4613da1cad2a28369aa78b69e87001ad9e9f 100644
--- a/base/message_loop/incoming_task_queue.cc
+++ b/base/message_loop/incoming_task_queue.cc
@@ -44,7 +44,8 @@ IncomingTaskQueue::IncomingTaskQueue(MessageLoop* message_loop)
       message_loop_(message_loop),
       next_sequence_num_(0),
       message_loop_scheduled_(false),
-      always_schedule_work_(AlwaysNotifyPump(message_loop_->type())) {
+      always_schedule_work_(AlwaysNotifyPump(message_loop_->type())),
+      is_ready_for_scheduling_(false) {
 }
 
 bool IncomingTaskQueue::AddToIncomingQueue(
@@ -109,6 +110,15 @@ void IncomingTaskQueue::WillDestroyCurrentMessageLoop() {
   message_loop_ = NULL;
 }
 
+void IncomingTaskQueue::StartScheduling() {
+  AutoLock lock(incoming_queue_lock_);
+  DCHECK(!is_ready_for_scheduling_);
+  DCHECK(!message_loop_scheduled_);
+  is_ready_for_scheduling_ = true;
+  if (!incoming_queue_.empty())
+    ScheduleWork();
+}
+
 IncomingTaskQueue::~IncomingTaskQueue() {
   // Verify that WillDestroyCurrentMessageLoop() has been called.
   DCHECK(!message_loop_);
@@ -148,19 +158,25 @@ bool IncomingTaskQueue::PostPendingTask(PendingTask* pending_task) {
   incoming_queue_.push(*pending_task);
   pending_task->task.Reset();
 
-  if (always_schedule_work_ || (!message_loop_scheduled_ && was_empty)) {
-    // Wake up the message loop.
-    message_loop_->ScheduleWork();
-    // After we've scheduled the message loop, we do not need to do so again
-    // until we know it has processed all of the work in our queue and is
-    // waiting for more work again. The message loop will always attempt to
-    // reload from the incoming queue before waiting again so we clear this flag
-    // in ReloadWorkQueue().
-    message_loop_scheduled_ = true;
+  if (is_ready_for_scheduling_ &&
+      (always_schedule_work_ || (!message_loop_scheduled_ && was_empty))) {
+    ScheduleWork();
   }
 
   return true;
 }
 
+void IncomingTaskQueue::ScheduleWork() {
+  DCHECK(is_ready_for_scheduling_);
+  // Wake up the message loop.
+  message_loop_->ScheduleWork();
+  // After we've scheduled the message loop, we do not need to do so again
+  // until we know it has processed all of the work in our queue and is
+  // waiting for more work again. The message loop will always attempt to
+  // reload from the incoming queue before waiting again so we clear this flag
+  // in ReloadWorkQueue().
+  message_loop_scheduled_ = true;
+}
+
 }  // namespace internal
 }  // namespace base